A typical low slope roof consists of the following components, from bottom to top (not including structural components of the building): deck system, insulation, and a waterproof barrier. The perimeter of the roof may be flat, have a parapet wall, or a combination of both. In the main field of the body of the roof, there can be any number of roof penetrations and other items, including such features as plumbing vent pipes, HVAC units on curbs or supports, expansion joints, conduit, or a wide variety of other items.
Singly ply membranes are rapidly becoming the most popular roofing system for buildings with low slope roofs. Single ply membranes include such materials as thermoplastics (TPO, PVC, CPE, among others) and rubber roof membrane (EPDM). These materials typically are packaged in roll form and are unrolled onto the roof during installation. The sides and ends of the rolls are overlapped and then joined via some form of adhesion (heat or chemical means are the most common) to form a larger, continuous sheet. The rest of installation depends on the means of waterproofing at through-roof penetrations and other rooftop structures but also includes an especially important step—securing the roof to the building's structure.
There are three primary means of securing a roofing system to a building's structure: mechanical fastening, adhering, or ballasting. Mechanical fastening involves passing fasteners through the membrane and substrate then into the decking material. This method is most common for roofs that are easily screwed into, i.e. wood or metal decks. Adhering involves gluing the roof system to the decking and is most common for roofs where the decking is not easily mechanically fastened to, especially in the case of concrete decks. Ballasting involves placing a fairly large quantity of small rock or pebbles on the membrane's surface. This method of securing the roofing system to the building works great in situations where one might not want or be able to mechanically fasten or fully adhere the system to the roof. Each of these methods secures the roof system to the deck and structure of the building, and each one can be used in a wide variety of instances, depending on the particular building's needs.
The most common types of decking for low slope roofs are: metal, wood, and concrete. Metal decking is comprised of sheets of metal that have been bent into a specific pattern in order to better support the weight of the roof. Wood decking is typically either sheets or planks of wood. Concrete decking is typically fairly thick (over one or two inches in thickness) and is either poured in place or set in pre-fabricated pieces. Though all of these types of deck are capable of receiving mechanical fasteners, it is a very simple process in wood and metal decks, while it is more difficult and labor consuming in concrete decks. Fastening into wood or metal simply requires screwing or nailing into it. Fastening into concrete requires pre-drilling the hole and then inserting a separate fastening mechanism into or through the hole. This process which is much more labor intensive and time consuming when one considers the large quantity of fasteners that must be installed on a roof to properly secure it with necessary wind uplift ratings.
Both the options of either fully adhering a roof system or ballasting a roof system carry with them disadvantages. For instance, it is not always possible to fully adhere a membrane system to a roof due to moisture content within an existing roof system (in the case of re-roofing over the existing roof) or even due to the fumes from the adhesives. Ballasting the roof involves a large quantity of the rock in order to provide sufficient downward force to resist wind uplift. This rock must be moved to the roof during installation, requiring many truckloads for larger roofs. Also, if the roof leaks after installation by ballasting, the repair process is not nearly as straightforward as the roof is hidden underneath a thick layer of rock. Both adhering and ballasting are highly labor intensive methods of roof installation and require other special details in order to complete the roofing system.
Oftentimes, regardless of the type of deck, fully adhering or ballasting the roof both are undesirable. If the deck does not easily receive mechanical fasteners, one would ideally like an option to still mechanically fasten but with a lesser number of fasteners. There have been previous inventions that have attempted to solve this problem. One of interest would be U.S. Pat. No. 7,028,438, which is a roofing system that utilizes hold down straps for insulation. In addition, others have used batten bars, which help to further secure the roofing membrane in locations linearly between the main fasteners. U.S. Pat. No. 6,764,260 uses this method. These prior methods fail to sufficiently improve the process of mechanically fastening a roof.